The polyphenylene ether resins are well known in the art as comprising a family of thermoplastic materials which are suitable for various engineering purposes. These may be made by catalyzed and non-catalyzed processes which are described in the patent literature, such as in Hay, U.S. Pat. Nos. 3,306,874 and 3,306,875, and in Stamatoff, U.S. Pat. Nos. 3,257,357 and 3,257,358, which are incorporated herein by reference.
It is known that the polyphenylene ether resins may be admixed with styrene resins, both unmodified and modified, to produce compositions having properties which are better than those of either of the two polymers individually. Such compositions are disclosed by Cizek in U.S. Pat. No. 3,383,435, incorporated herein by reference.
It is known that compositions containing a polyphenylene ether resin can be improved by including polystyrene which has been modified by EPDM elastomers. Such compositions are disclosed by Abolins and Cooper, in U.S. Pat. Nos. 3,943,191, 3,959,211 and 3,974,235 (EPDM rubber having a low degree of unsaturation); by Abolins, Cooper and Lee, Jr., in U.S. Pat. No. 3,981,841 (includes emulsion-graft EPDM-styrene copolymer); by Cooper and Haaf, in U.S. Pat. No. 4,172,826 (small particle size EPDM together with hydrogenated triblock); by Cooper and Katchman, in U.S. Pat. No. 4,101,503 (small particle size EPDM rubber in which the styrene resin has a high molecular weight), in U.S. Pat. No. 4,101,504 (in which the EPDM rubber content is at least 8 percent by weight); in U.S. Pat. No. 4,101,505 (containing at least about 2 percent by weight of a toluene-insoluble gel); in U.S. Pat. No. 4,102,850 (small particle size EPDM rubber together with mineral oil); in U.S. Pat. No. 4,139,574 (EPDM rubber in combination with hydrogenated radial teleblock copolymer); and in U.S. Pat. No. 4,152,316 (the EPDM rubber has a particle size of less than about two microns); by Katchman, in U.S. Pat. No. 3,960,808 (EPDM modified styrene resin in combination with unmodified styrene resin); and by Lee, Jr., in U.S. Pat. No. 4,143,095 (EPDM rubber modified styrene resin in combination with hydrogenated triblock).
It has been disclosed by Abolins and Reinhard, in U.S. Pat. Nos. 3,792,123, 3,833,688 and 3,983,090, that compositions containing a polyphenylene ether resin can be modified for improvements in the toughness and resistance to aggressive solvents by including certain acrylic resin modified diene rubber-containing resins.
It has more recently been proposed that compositions comprising a polyphenylene ether resin and a homopolystyrene can be modified by including a copolymer of styrene and butyl acrylate. Although significant improvement in the flow properties was observed, it was also found that the improvement in the impact resistance was disappointingly small.
It has now been discovered that if a copolymer of styrene and butyl acrylate is included in a composition comprising a polyphenylene ether resin and an EPDM modified polystyrene, the resulting composition possesses enhanced impact resistance, good flow properties and satisfactory thermal stability.